Polyolefin resins such as polyethylene and polypropylene are extensively used as materials for shaped articles such as fibers, films, sheets and other articles, as having excellent physical, chemical and electrical properties. However, such polyolefin resins have a problem that they are deteriorated by the action of heat, oxygen and light so that the mechanical properties are thereby lowered.
In order to prevent such deterioration, various stabilizers have heretofore been used. For instance, it is known to use various phenolic compounds, such as:
2,6-di-t-butyl-4-methylphenol; PA0 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate; and PA0 dilauryl thiodipropionate; PA0 dimyristyl thiodipropionate; and PA0 pentaerythritol tetrakis(3-dodecylthiopropionate). PA0 Bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite; PA0 Tris(2,4-di-t-butylphenyl) phosphite; PA0 Bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite; PA0 Distearyl pentaerythritol diphosphite; and PA0 Tetrakis(2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphonite.
t e t r a k i s [3 - ( 3 , 5 - d i - t - b u t y 1 - 4-hydroxyphenyl)propionyloxymethyl]methane,
for the purpose of preventing deterioration of polyolefin resins by heat and oxidation. In addition, for the purpose of further improving the anti-oxidant property of such phenolic compounds, it is also known to use, together with them, sulfur-containing compounds such as:
On the other hand, for the purpose of preventing deterioration of the resins caused by light, it is known to use various light-resisting agents, for example, benzophenone compounds, benzotriazole compounds, nickel-chelate compounds and hindered amine compounds, singly or in combination of two or more of them. Further, various proposals of combining such known stabilizers have also been made.
However, although the polyolefin compositions which have heretofore been proposed could give favorable results which would be satisfactory in some degree with respect to the stability against heat, oxidation and light, they still have some problems in the field where the shaped articles such as fibers and films are exposed to severe conditions of production and use. Under this situation, they could not be said t be always sufficient and satisfactory in practical use.
For instance, with respect to fibers as one example of the shaped articles, the conditions of producing and working them are severer than any other general thick articles and therefore they must first be resistant to a high temperature in the production step. In the drying step after the fiber formation, a city gas or kerosene is often used as a heat source. As the fibers would easily be discolored by the combustion gas from the heat source, they are desirably also resistant to such discoloration. Further, even after the fibers have been made into fibrous products, the products are also exposed to exhaust gas, such as combustion gas from fuel of cars outdoors as well as combustion gas from oil stoves indoors. Under these conditions, since the products are easily discolored by NOx gas in the exhaust gas, they are also desirably resistant to such discoloration.
Despite the current situation mentioned above, the polyolefin compositions which have heretofore been proposed could not be said to be sufficiently stable against discoloration caused by combustion gas and NOx gas, though they would be stable at least against heat, oxidation and light. Therefore, it has been strongly desired to develop stabilizer systems which are effective not only for stabilizing polyolefin compositions against heat, oxidation and light but also for satisfactorily stabilizing them against discoloration caused by combustion gas and NOx gas.